#include <bits/stdc++.h>
#define rep(i,n) for(int i=0;i<(int)n;i++)
using namespace std;
using ll = long long;
using P = pair<int, int>;

int main() {
    ll x, y, d;
    cin >> x >> y >> d;
    x = min(x, d), y = min(y, d);
    cout << max((ll)0, min(d + 1, x + y + 1 - d)) << endl;
    return 0;
}